1. Technical Field of the Invention
The present invention relates generally to a fuel injector to be mounted in an internal combustion engine to spray fuel thereinto, and more particularly to such a fuel injector which has installed therein a fuel pressure sensor working to measure a change in pressure of the fuel arising from the spraying of the fuel into the engine and which is designed to minimize mechanical stress on the fuel pressure sensor.
2. Background Art
In order to ensure the accuracy in controlling output torque of internal combustion engines and the quantity of exhaust emissions therefrom, it is essential to control a fuel injection mode such as the quantity of fuel to be sprayed from a fuel injector or the injection timing at which the fuel injector starts to spray the fuel. For controlling such a fuel injection mode, there have been proposed techniques for monitoring a change in pressure of the fuel upon spraying thereof from the fuel injector.
Specifically, the time when the pressure of the fuel begins to drop due to the spraying thereof from the fuel injector may be used to determine an actual injection timing at which the fuel has been sprayed actually. The amount of drop in pressure of the fuel arising from the spraying thereof may be used to determine the quantity of fuel actually sprayed from the fuel injector. Such actual observation of the fuel injection mode ensures the desired accuracy in controlling the fuel injection mode.
For instance, in the case where a change in pressure of the fuel arising from the spraying of the fuel from the fuel injector (which will also be referred to as a fuel pressure change below) is measured using a pressure sensor installed directly in a common rail (i.e., a fuel accumulator), it will be somewhat absorbed within the common rail, thus resulting in a decrease in accuracy in determining such a pressure change. In order to alleviate this drawback, Japanese Patent First Publication No. 2000-265892 teaches installation of the pressure sensor in a joint between the common rail and a high-pressure pipe through which the fuel is delivered from the common rail to the fuel injector to measure the fuel pressure change before it is absorbed within the common rail.
The fuel pressure change, as produced at a spray hole of the fuel injector through which the fuel has been sprayed, will, however, surely attenuate within the high-pressure pipe. The use of the pressure sensor installed in the joint between the common rail and the high-pressure pipe, therefore, does not ensure the desired accuracy in determining the fuel pressure change. The inventors have study the installation of the pressure sensor in a portion of the fuel injector which is located downstream of the high-pressure pipe. Such installation, however, has been found to pose the problems, as discussed below.
The pressure sensor is typically made up of a body in which a high-pressure path is formed to supply high-pressure fuel to a spray hole and a valve actuator installed in the body to move a valve to open or close the spray hole. The body is usually subjected to various external pressures as well as internal pressure exerted by the fuel.
For example, when a fuel injector is, as illustrated in FIG. 4, pressed and held by a clamp Kin an internal combustion engine with an injector body 4x fit in a mount hole E3 of a cylinder head E2 of the engine, it will cause the pressure F1 to continue to be exerted by the clamp K on the injector body 4x in a vertical direction. Additionally, a high-pressure pipe HP which supplies the high-pressure fuel to the fuel injector is joined to an inlet of the injector body 4x in misignment therewith, it will cause the pressure F2 to be exerted by the high-pressure pipe HP on the injector body 4x. 
The exertion of the pressure F1 or F2 from the high-pressure pipe HP will cause internal stress to increase, which acts on a fuel pressure sensor 50x installed in the fuel injector, thus resulting in a decrease in accuracy in measuring the pressure of fuel.